[crater]

> So they'd have to send you an update to your mobile device, which now creates more questions like, how to communicate to the person in line that's been waiting for 15 minutes that no, you are not cutting in line.

Something like a pick-up window would work.

> do you show your phone to the person and hope they have good organization of orders pending pickup?

In my opinion, if the food truck has implemented this Square software, they might keep "organization of orders pending pickup" in mind. Showing your phone to the person should be enough, (with some sort of simple identification on the phone message).

I don't know if Square Pickup does this but I'm just arguing against your doubt that it wouldn't work.

[awad]

I used Paypal to pay for something in-store recently and they identified me by matching the selfie that I took in the app (that showed up on their iPad screen tied to my name) to the same one shown on the app on my phone that I held up for them. Pretty neat/clever and would work just as well here.